Biology, Morphometric Characteristics and Life Table Parameters of the Pulse Beetle, Callosobruchus maculatus (Fabricius) on Green Gram under Laboratory Conditions
Abstract
Background: The pulse beetle Callosobruchus maculatus (Fabricius) is a major pest of stored green gram, leading to significant losses in seed quantity and quality. This study looked at the developmental biology, morphological characteristics, reproduction, sex ratio and population growth of C. maculatus reared on green gram in controlled lab conditions (28 ± 2°C and 65-75% relative humidity. Methods: The study was carried out under controlled laboratory conditions using a standardized culture of C. maculatus maintained on green gram, where developmental stages, morphometric traits, reproductive parameters and life table data were recorded through systematic observations of individually reared cohorts. Results: The eggs hatched within 5 to 7 days. The larval stage lasted for 15 to 22 days followed by the prepupal and pupal stages, which lasted 1 to 2 days and 5 to 8 days, respectively. Adult males lived between 8 and 13 days, while females lived for 10 to 15 days. Generally, females lived longer. The average fecundity was 76.8 eggs per female and the emerging population had a female-biased sex ratio of 1:1.3. Size analysis showed a steady increase in body size across successive instars and clear differences between male and female adults. Life-table analysis indicated that the highest mortality occurred during the transition from the egg stage to the early larval stage, accounting for about 19% mortality. Life expectancy declined progressively with age, decreasing from 23.30 days at egg hatch to 2.50 days by 36-40 days. Population growth parameters showed a net reproductive rate (R0) of 9.52, an intrinsic rate of increase (rm) of 0.0895 and a finite rate of increase (λ) of 1.09, suggesting a strong potential for population growth on this host. Overall, the findings indicate that green gram provides favourable conditions for the development and multiplication of C. maculatus, emphasizing the need for effective pest management strategies after harvest.